Our principal research objectives are to identify the biochemical and physical structure of the light scattering elements in the cataractous lens and to determine their biochemical origin. We have established by in vitro methods the presence of a soluble heavy molecular weight component (HM) in human normal and cataractous lenses. This component increases with age and comprises a significant fraction of the nuclear portion of nuclear sclerotic lenses. Recently, we discovered that it is possible to measure the diffusion coefficient in the whole intact human lens by measuring the spectrum of laser light scattered from the lens. These in vivo methods demonstrated that human cataractous lenses contain proteins whose size is considerably larger than that found in the normal lens. Having established by both in vivo and in vitro methods that aggregation plays a key role in cataract formation, we are now in a position to identify both biochemically and optically the detailed molecular alterations that lead to aggregation and thus to cataract disease.